Several video compression specifications have been developed under the auspices of the Motion Picture Expert Group (“MPEG”), such as MPEG and MPEG-2. An MPEG signal has six layers of syntax. These are a sequence layer, a group of pictures (“GOP”) layer, a picture layer, a slice layer, a macroblock layer, and a block layer. A video signal is a stream of pictures or frames. Each picture is represented by a predetermined number of picture elements (“pixels”) per line and lines per picture. Pixels are coded as luminance and two color difference components, generally denoted as Y, CB, and CR, respectively. Pictures are generally broken up into “blocks.” Blocks are rectilinear groups of pixels, generally 8 by 8 in number.
A GOP is a set of pictures or frames that starts with an I-frame and includes P-frames and/or B-frames. An I-frame (intra frame) or Intra-picture (I-picture) is encoded using only information available within that frame (intra coding). The coding of I-frames results in the most bits compared with P-frames and B-frames. A P-frame (predicted frame) encoding uses motion compensated information relative to a previous I-frame or P-frame. A B-frame (bidirectional frame) encoding uses motion compensated information relative to both a preceding frame and a following frame as reference frames.
A video encoder compresses a video signal for more efficient transmission and storage. This saves bandwidth in transmission or memory in storage. Additionally, depending on the parameters used during video encoding, a signal can be tailored for display on a specific end display device. By way of example, different devices generally have different display resolution capability and different bit rate capability. By proper selection of the processing parameters, an encoded video signal can be tailored for decoding and display on any given display device.
Increasingly, video systems in businesses, schools, universities, homes, and so forth, for example, have multiple display devices which may need to display the same video stream simultaneously. Traditionally, this was accomplished by simply fanning out the same video signal to all the selected display devices. In cases where video signals having different encoding characteristics are required, the traditional solution is to employ separate video encoders, one for each different encoding of the video signal, which is expensive due to the multiplicity of hardware.
The present invention advantageously addresses the above needs and other needs.